Deployable booms are widely used in portable antennas, for use on the ground and for use in space. When they are deployed they have a length wh.+-.ch does not permit them to be transported, or to be subjected to stringent forces. For this reason they are made retractable to a shorter length and are latched in the resulting smaller envelope for transportation on the ground, and for security during launch and airborne and space vehicles.
One weII-known deployable boom is shown in U.S. Pat. No. 38486279 issue to James, E. Webb of NASA. This boom is characteristic of the type. It includes longerons which can be folded or bent to permit the shorter length retracted configuration, and which when deployed are braced by transverse members to resist axial collapse and bending forces.
It is evident that booms of this type must be storable in a compact, retracted configuration, and deployable to an extended, deployed configuration, the two configurations being appropriate to conditions to which the boom will be subjected at different times. The boom will be retracted during transportation and storage. It wilI be extended during use, for example as a stationary support for an antenna. It often is adapted for rotation, especially when used to support instruments or solar energy panels.
Arrangements for initial Iatching of the boom in its retracted condition are well known. So are arrangements to permit the unlatching and controlIed extension of the boom. However, known arrangements have generally been one-shot. Especially for space vehicles it was sufficient for the boom to be transportable to and mounted to the vehicle be reliably latched for the launch conditions, and then to be deployed. Once deployed it was simply left there, because the vehicle was not expected to return. The terms "extended", "expanded" and "deployed" are interchangeably used herein.
With the advent of the space shuttle, this arrangement was no longer aooeptable. After its use in space, the boom would have to be returned to its retracted position and re-Iatched in order to survive re-entry and landing. This imposes an entirely new set of design restraints on the system. It now must reliably latch, unlatch, deploy, retract and relatch. Because the cost to launch weight into space is so very large, a conventional approach to provide separate Iatching and deployment controls would be at least very disadvantageous.
It is an object of this invention to provide an elegantly simple system which is bi-directionally operable to latch, unlatch, deploy, retract and reIatch the boom with a single motor and single drive. It is so reliabIe that the motor to drive tbe system can even be removed and used for another purpose, or merely be stored separately, while the boom is either in its retracted or deployed configuration.